1. Technical Field
Exemplary aspects of the present disclosure relate to a fixing device for use in an image forming apparatus such as a printer, a facsimile machine, a copier, and the like, and further to the image forming apparatus including such a fixing device.
2. Related Art
For fixing devices employed in image forming apparatuses a thin-layered fixing belt formed of a metal base and a resin rubber layer deposited on the metal base is known. Use of such a thin-layered fixing belt with a low thermal capacity can drastically reduce the power necessary for heating the fixing belt and warm-up time or a first print time. The first print time is the time required from receipt of a print request to a completion of a printing operation and a sheet discharge.
For example, a fixing device includes an endless fixing belt and a pressure roller. The pressure roller contacts an outer circumference of the fixing belt. A nip-forming member is disposed at an inner circumference of the fixing belt that presses against the inner surface of the belt to form a nip portion with the pressure roller, with the fixing belt in between.
A heat source to heat the fixing belt with radiant heat is disposed at an interior side of the fixing belt. In this case, because the endless belt can be directly heated by the heat source where the nip-forming member is not disposed, heating efficiency is drastically improved and energy consumption is reduced, so that the first-print time from standby is further shortened.
When a sheet of paper passes through the nip portion of the fixing device, because the fixing belt and the sheet contact each other, the heat of the fixing belt is absorbed by the sheet. On the other hand, since the fixing belt is wider than the sheet, beyond the margins of the sheet, the fixing belt and the sheet do not contact each other and the heat is not absorbed by the sheet. As a result, when a number of sheets are conveyed continuously, heat accumulates in this so-called non-sheet passing area, degrading the fixing belt.
The fixing device includes a shielding member that shields radiant heat from the heat source, disposed between the heat source and the fixing belt at both lateral sides the fixing belt. With this structure, an excess temperature rise of the fixing belt in the non-sheet passing area thereof is prevented, and the degradation of the fixing belt due to the excess heat is prevented.
However, because the heat-shielding member itself is heated by the radiant heat from the heat source, the shielding member tends to get overheated during the continuous printing of the number of sheets, resulting in deformation of the shielding member due to the excess heat. Such deformation of the shielding member may cause degradation of the function of the shielding member or interference of the deformed portion of the shielding member with another part or component.